1. Field of the Invention
This invention relates to backing paper for roll film, and more particularly to backing paper for roll film having improved light-shielding properties, moisture resistance, dimensional stability, and so forth.
2. Description of the Prior Art
Light-shielding papers usually used include black-colored paper, paper including a colored paper layer, and paper produced by providing a light-shielding layer on a sheet of paper having no or insufficient light-shielding properties. They are provided with letters or figures for indication of their functions or printed to increase their product values. In some cases, a protective layer may be provided on one or both surfaces of the light-shielding paper.
These light-shielding papers are used in various forms, for example, as wrapping paper for light sensitive photographic material and backing paper for roll films. This invention is directed to backing paper for roll films, which is hereinafter referred to merely as "backing paper".
This backing paper is overlaid on a given length of photographic film and wound around a core, or when a core is not used, it is wound up and placed in an appropriate size holder. The backing paper has a limited thickness because its length is fixed; for instance, the standard for thickness could be 0.10 (+0.02, -0.01) mm using JIS K-7512-1961, 0.0041(.+-.0.0006) inch under American National Standard PH 1.21-1972, or 0.1 (+0.02, -0.01) mm under DIN 4523 Teil 1.
Referring to FIGS. 15 and 16, conventional backing papers are generally provided with light-shielding properties by incorporating carbon black or yellow pigment in a support 3' or by providing a protective layer 1' containing carbon black or yellow pigment on the support 3'. In these figures, the reference numerals 1 and 2 indicate a protective layer and a print layer, respectively.
Japanese Patent Publication No. 49205/76 discloses a backing paper produced by providing on at least one side of paper a film of a copolymer of ethylene and at least one of acrylate ester and methacrylate ester in which carbon black has been dispersed; Japanese Patent Application (OPI) No. 150016/77 ("OPI" indicates a published unexamined Japanese patent application) discloses a backing paper produced by providing a carbon black-dispersed light-shielding layer on a white support; and in U.S. Defensive Publication No. T871,004 a backing paper is disclosed produced by providing a plurality of carbon black layers on a paper support.
These conventional backing papers, however, have the following defects:
(1) When they are allowed to stand at high temperatures and humidities (for example, at 50.degree. C. and 80% for 3 days), adhesion of the backing paper and the film occurs because of their insufficient moisture resistances.
(2) When they are allowed to stand in the air for a long period of time, fogging of the film occurs due to gases: this so-called gas fogging takes place because of their insufficient gas-shielding properties.
(3) For a backing paper consisting of a paper support and a plastic film layer, loose winding of film occurs (i.e., spaces occur between the successive layers of the rolled film) because of the backing paper's high bending strength, and therefore difficulties are encountered in fitting the roll into a camera.
(4) For a backing paper comprising mainly paper, the dimensional stability is low because of large elongation due to moisture.